Streptococcal diseases are among the most common bacterial infections in man. One approach to the control of infectious diseases is the use of antibacterial drugs. Our studies have previously identified three tetracycline resistance determinants and have shown that two of these determinants (tetM and tetN) mediate resistance by a novel mechanism involving a cytoplasmic factor which associates with ribosomes and renders protein synthesis resistant to the drug. The tetM determinant may be particularly significant in chemical terms since it has been identified in a number of other bacterial pathogens. Elucidation of the basis of tetM mediated resistance will provide information not only about this resistance mechanism but also about ribosome function and response to antibiotics during protein synthesis. We will purify the resistance factor and characterize its interaction with ribosomes and investigate the biochemical basis of tetM action. The tetN determinant will be cloned and the resistance region defined using deletion analysis and insertion mutagenesis. The tetN gene products will be analyzed in minicells and by in vitro translation. Vaccines are also useful in control of infectious diseases. M- protein is a surface protein associated with virulence of group A streptococcus and antibodies directed against this protein protect the host against subsequent infection by the same group A streptococcal serotype. To begin molecular characterization of this protein, we have cloned and sequenced the serotype 24 M- protein gene of group A streptococcus. The mature M-protein is novel in that it contains several highly conserved repeated sequences; the carboxyl terminal portion of the protein is also conserved among different serotypes. These latter regions of the M-24 protein can be specifically overproduced and tested for their ability to elicit protective antibodies against a variety of M- protein serotypes.